Household willingness to pay for water supply improvements: A meta-analytical assessment

Monetary willingness to pay (WTP) is widely used to value improvements in water services, yet comparisons across populations are complicated because observed WTP may reflect both households' ability to pay and the magnitude of the service improvement they stand to gain. This study examines these two mechanisms through a systematic review and dependency-aware meta-analysis of 68 WTP estimates from 42 studies published since 2009. All estimates are standardized to monthly household WTP in real 2024 PPP-adjusted USD and analysed using a three-level restricted maximum likelihood (REML) meta-regression that accounts for effect-specific sampling uncertainty, dependence among estimates from the same respondent sample, and heterogeneity within and between studies. Household income is a strong and robust predictor of WTP, with an estimated income elasticity of 0.339 (95% CI 0.178 to 0.501). Independently of income, households with better initial water-service conditions are willing to pay substantially less for further improvements than households facing the poorest service conditions, consistent with a declining marginal value of additional service gains. Direct household connections and private provision are also positively associated with WTP, although these findings are less consistent across sensitivity analyses. We find no evidence of a persistent post-COVID increase in WTP. Overall, cross-context differences in WTP reflect both purchasing power and the magnitude of existing service deficits. This distinction is important for benefit transfer and water-investment appraisal because raw monetary WTP may understate the welfare value of service improvements in lower-income populations.